1. Field of the Invention
The present invention relates to thermoplastic concentrates containing a high concentration of inorganic pigment and a method for their production. More specifically, the present invention relates to surface treatment of inorganic pigments for improved dispersibility in thermoplastic resins. Most specifically, the present invention relates to treating titanium dioxide pigments with a partial ester polyol and unsaturated monocarboxylic acid for increased concentration and dispersion in polyolefin resins.
2. Description of the Prior Art
Inorganic pigments, such as titanium dioxide for example, are used in a variety of thermoplastic resin-based consumer goods. It is known, however, that the quality of the properties that the inorganic pigment imparts to the resin, such as opacity, color, brightness, UV and thermal stabilization, and the like, depends significantly on how evenly and uniformly the pigment is dispersed in the resin, as well as on the amount of pigment that can be effectively incorporated into the resin. It is also known that the hydrophobic nature of such thermoplastic resins is incompatible with the hydrophilic nature of such inorganic pigments thus making it difficult to obtain good dispersion of the pigments in the resins, especially at high pigment concentrations greater than 50 percent by weight, as pointed out in U.S. Pat. No. 4,183,843, which disclosed the use of a polar phosphate ester surfactant on alumina trihydrate to lower the viscosity of polyester inorganic filler composites.
The chemical surface treatment of inorganic pigments to improve dispersibility in, and increase compatibility with, thermoplastic resins, is known in the art. For example, U.S. Pat. No. 4,209,430 discloses the treatment of inorganic pigments with phosphorylated polyenes, which are the reaction products of a phosphorylating agent and a polyolefinically unsaturated compound of at least 10 carbon atoms. The pigments thus treated are described as possessing improved pigment properties as well as improved dispersibility and a reduced tendency to yellow in thermoplastic polyolefins in which the treated pigments are dispersed.
U.S. Pat. Nos. 4,357,170 and 4,377,417 also disclose inorganic pigment treatments for reducing the yellowing tendency of polymeric compositions containing such pigments. According to these patents, treating pigmentary titanium dioxide with an additive system comprised of an organophosphate/alkanolamine addition product, alone or in combination with a polyol, results in a reduction of the tendency of the treated pigment to yellow in polymeric compositions. These patents, however, do not mention any improved dispersibility benefit afforded by such treatment.
Examples of inorganic pigment treatments to which improved dispersibility benefits have been ascribed include the treatment disclosed in U.S. Pat. No. 5,288,320, which is identical to GB patent No. 2,252,306. These patents teach the treatment of titanium dioxide with an ester or partial ester of a hydroxy compound containing from 1 to 6 hydroxyl groups and an aliphatic saturated monocarboxylic acid having between 10 and 12 carbon atoms. Also, U.S. Pat. No. 3,728,142 discloses the treatment of inorganic pigments with non-drying fatty acid-modified alkyd resins for improved pigment dispersibility in plastics. A further example of the surface treatment of inorganic pigments for improved dispersibility is found in U.S. Pat. No. 3,754,956, which discloses the treatment of titanium dioxide pigments with a liquid polylactone having terminal hydroxy groups. Still another method of treating titanium dioxide pigments to achieve good dispersion and optical properties is described in U.S. Pat. No. 4,235,768, which discloses the art of treating titanium dioxide pigments with an aqueous polymer solution containing carboxyl groups. Also, U.S. Pat. No. 5,318,625 teaches the treatment of inorganic pigments with organophosphate esters for improved dispersibility and for production of polymeric concentrates.
None of the aforementioned patents teaches either the treatment of inorganic pigments with a partial ester polyol and unsaturated monocarboxylic acid or the production therefrom of the thermoplastic concentrates which are the subject of this application.